A pressure sensor, especially a differential pressure sensor, includes a platform, at each end of which is attached an advantageously circularly-shaped membrane, or diaphragm, with formation of a pressure chamber between the platform end surface and the membrane. The two pressure chambers are coupled together over a hydraulic path, with the pressure chambers, the hydraulic path, and possible other sections communicating with them being filled with a hydraulic liquid. For operating the pressure sensor, it is necessary to place a liquid quantity defined as exactly as possible in the hydraulic system composed of the two pressure chambers, the hydraulic path, and the possibly present, communicating sections. For this purpose, for example, the hydraulic system is completely filled with a hydraulic liquid, and a steel sphere of diameter greater than the inner diameter of the filling nozzle is pressed into the filling nozzle, where it remains lodged under plastic deformation of the wall. In this way, the hydraulic system is sealed, but there is variation with respect to sphere position and the trapped amount of liquid. Moreover, this sealing of the pressure sensor is little suited in the case of platforms made of ceramic.
In another solution of the prior art, the filling nozzle of the hydraulic system has an outer section with a first radius, which is greater than the radius of a sealing sphere, and a second section with a smaller radius than the radius of the sealing sphere, so that, at the transition between the first section and the second section, an abutment surface is formed, which can be sealed by the sphere. The sphere is fixed in this position with a screw, which engages a thread formed in the wall of the first section of the filling nozzle.
This solution is complicated to build, as regards providing the thread. Moreover, it leads to small variations in the trapped volume, since the sphere surface or the abutment surface can be elastically, or plastically, deformed as a function of the bearing pressure of the screw.